1. Field of the Invention
The present invention relates to a display screen control system, and more particularly to a display screen control system for use in a terminal device having an on-line function for transferring data between a central processing unit and the terminal device and an off-line function for independently processing data by the terminal device, such as document preparation.
2. Description of the Prior Art
As the are of office automation OA develops, a documentation preparing device, such as a word processor and an off-line document processing device having a document preparation function in addition to a conventional online function of an office computer, have been put into practice as OA office equipment. In such equipment, an operation will operate keys while he or she watches a display screen.
In the prior art devices of this type, however, the on-line processing and the off-line processing cannot be carried out in parallel even in a device having an on-line data processing capability. The on-line function, if any, can be utilized for a relatively simple purpose, such as for batch-transferring document data prepared by the off-line processing to the central data processing unit. Accordingly, it is not possible to refer, on a real time basis, to the document data possessed by the central data processing unit in the course of the preparation of the documentation by the off-line processing by the terminal device and utilize a portion of the document data for the document being prepared, and hence the large amount of the power of the central processing unit is not fully utilized.